Dry-Farming in California's Drought, Part 1: Understanding California's Only-Sorta-Mediterranean Climate

Over the last few months, it seems like everyone I meet, whether locally or around the country, is wondering how we're doing in what our governor has termed a "historic drought".  Many are surprised to hear that while we're watching it warily, we think we're in OK shape.  And even more are surprised to learn that a critical reason why we think we're OK is that we've been increasingly investing in dry farming over recent years.  It seems counter-intuitive that farming without irrigation makes you better able to survive periods with less rainfall, but it is, we think, an important part of the answer.  In this three-part series, I'll look at California's drought from our perspective.  This first part will look at the differences between the Mediterranean climate and our climate here in California, and what lessons we took from that.  The second part looks both at how our original approach to farming has set our vineyard up to succeed through the last four dry years and what we're changing to adjust to what will likely be a drier future.  Finally, the third part looks back historically at how grapevines -- which should be one of the easier crops to dry-farm -- came to be so widely irrigated in California. 

We are, of course, inspired by Chateauneuf-du-Pape, the home of our founding partners at Beaucastel.  In Chateauneuf, as in most top winemaking regions in France, irrigation is prohibited.  This prohibition is enforced to prevent dilution and overproduction, and to encourage deeper rooting which should help wines express their region's terroir.  We came into our project believing that dry-farming would give us our best chance to express our terroir, although we were unsure whether we would be able to right away.

Chateauneuf-du-Pape receives, on average, 723mm (28 inches) of rain per year. The distribution is relatively constant, except for somewhat drier summers and somewhat wetter falls. Still, it can rain any time during the year. The chart below (which I found, along with the data above, on the useful site climate-data.org) shows the distribution of rainfall by month, with January (01) on the left and December (12) on the right:

Our area west of Paso Robles has received historically a similar amount of precipitation annually (about 28 inches) but it is much more heavily weighted toward winter, with May-October almost entirely dry:

(Note that if you're looking at statistics for Paso Robles, you'll see that the town averages 14 inches of rain.  However, our weather station, here 12 miles west of town, has recorded over the last decade almost exactly double the rainfall measured in town, with very similar distribution.)

Otherwise, the climate is broadly similar, though somewhat more extreme here.  Average temperatures are a touch cooler here in summer and fall because of our cool nights, and a touch warmer in winter, because of our warm days.  Year-round we have a larger diurnal shift (the difference between the daytime high and the nighttime low) than does Chateauneuf, which produces more frosty winter nights and a greater chance of spring freezes, but also ensures that we maintain good acids during the growing season.  We receive a bit more sun.

Still, the primary difference between the two places, and the one that requires us to adjust most, is the distribution of the rainfall. We knew that we had chosen soils that were primarily calcareous clay, renowned for their water-holding capacity.  But still, it was clear to us that while we had enough rainfall on an annual basis to support dry-farmed grapevines, we would need to figure out how to get them through a five-month dry spell unlike anything they see in the Rhone Valley.  

What did we do?  Check out part 2.